DE 43 24 635 A1 describes microwave chamber ovens which are equipped for the batch sintering of ceramic bodies at temperatures up to approximately 1650.degree. C. Tunnel furnaces with conventional heating for continuous sintering are known, but they have proven to be energy consuming and time consuming. In order to alleviate this situation, a sintering installation has been proposed which comprises at least one stationary sintering table whereupon the bodies to be sintered can be placed, and at least one microwave source in a tunnel-shaped traveling hood, which can be moved by a drive over the sintering table. The hood is made in a self-supporting manner of metal, for instance aluminum. In a concrete example in or on the hood several microwave sources are provided, which are connected with a measuring, control and adjustment unit for the purpose of a temperature-controlled adjustment of the microwave output and/or of the hood speed. The ceramic bodies to be sintered can be arranged in a microwave-transparent and heat-insulated cassette, which for instance is made of aluminum oxide fiber.
DE 36 43 649 A1 also describes a device for the continuous heating of polar, especially temperature-sensitive goods or highly viscous products under simultaneous application of microwave energy and conditioned atmosphere, whereby the goods to be treated traverse a sufficiently dimensioned resonator chamber more than once in alternating directions. The transport of the goods through the device can be done optionally with the assistance of conveyor belts, troughs, spirals or pipes, with or without additional vibration, optionally with underpressure, normal pressure or overpressure. By increasing the resonance chamber, such a device should provide a more uniform field distribution, however any solid coupling of a test sample of hard metal, cermet or ceramic subjected to the heat of the microwave, modified the field distribution uncontrollably, especially then, when according to DE 36 43 649 A1, the pieces assume more or less randomly arranged positions when they fall from one conveyor belt unto the next.
DE 41 36 416 A1 proposes a device for the microwave treatment of materials, particularly starting materials for ceramic materials, alloys, etc. with a conveyor segment, which is defined at least sectionally by trough or pipe arrangements, whose walls have a certain microwave-absorption capability. This device has a resonator surrounding the wall at least sectionally, as well as at least one generator for producing microwave radiation, whereby the walls of the through or pipe arrangement have a microwave-absorption capability which varies over their length. For the purpose of directly heating the materials with microwaves, it is possible to precede the conveyor segment with an additional device, by means of which additives with high microwave-absorption capability are added to the materials. However this device is limited to the treatment of such materials which can be processed by an extruder or can be fed via a screw transporter.
DE 39 26 471 A1 describes a method for the heat treatment of organic substance mixtures, whereby the exposure to microwaves takes place within a resonance chamber which basically is reflectively limited on all sides, wherein a mode and frequency splitting of the microwave takes place and whose main dimensions do not fall below approximately eight times the free space wavelength of the microwave field in relation to the nominal frequency. Besides the fact that in this reference the treatment of hard metals, cermets and/or ceramics is not even mentioned, the expensive manufacturing techniques and required apparatus for the sintering treatment would be uneconomical in view of the low throughput.